Restoring our Rivers – ‘After the Fire’, is a practical, focused response designed to help landholders grapple with the immense damage sustained to their properties as a result of a fire storm, followed by a mass erosion event, which swept through parts of the Upper Murrumbidgee earlier this year.  By supporting landholders through the installation of erosion structures to prevent high amounts of sediment and ash entering the river, the project will provide people with the reassurance that they are not alone in facing the devastation the fires left behind.  The proposed works will also prevent vast amounts of sediment and ash entering the river, smothering fish habitat, reducing water quality and threatening decades of river restoration work.   Recovering our Rivers – ‘After the Fire’ will also be working in areas of the river that were not directly impacted by the fire but, with the advent of rain, are likely to be choked with ash and sediment flowing downstream.  The area we have chosen to work in has a population of nationally endangered Macquarie Perch and Platypus that require protection.

Our work in this project will focus on three key activities – erosion control, sediment control through willow removal and revegetation, and the provision of fish habitat.

Emergency erosion control structures

Some of the work to be undertaken will be in reaches of the river directly impacted by the fire and the massive erosion event that followed.  It is here that the majority of the costs in the project will be allocated against the following works

The fire, which impacted the steep and rugged upper Murrumbidgee River corridor just north of Bredbo in February 2020, was so intense that only bare soil remained.  During such events the chemical nature of the soil is altered so that it becomes water repellent, with the lack of vegetation reducing the infiltration capacity of the soil even further.  The rain event which extinguished the fire resulted in a mass erosion event which mobilised ash and sediment, and was assisted by the steepness of the terrain.   New erosion scours, the remobilisation of existing headcuts, and the dumping of massive amounts of gross sediment (sand and ash) in the base of tributary gullies to the river, now pose an ongoing threat to water quality (due to fine sediments and ash) and fish habitat (smothering refuge holes and breeding sites by sand slugs).

Restoring our Rivers – ‘After the Fire’ will address water quality decline by remediating three sites on two properties- a severely scoured gully floor eroding through an alluvial terrace, and a sediment control structure to hold back sediment further up on the same tributary gully and which is at risk of being washed into the river.  We will also treat an erosion headcut on a tributary gully on another property.  These works are a priority, as the catchment still struggles to recover ground cover and there is a high risk of further erosion during a heavy rain event.  Small rain events are showing us that the sand which is currently deposited in the tributary gullies is already being remobilised.

These works will protect priority fish habitat in the upper Murrumbidgee, including two natural populations of threatened native fish – namely Macquarie perch and Murray cod.  The work will also prevent further sediment entering the river which is one of the source catchments of Canberra’s drinking water supply.

Sediment control through strategic willow removal

Macquarie perch are an endangered native fish that require good quality water flowing over shallow rock riffles and native riparian habitat. In this stretch of reach works Restoring our Rivers – ‘After the Fire’ will address the increasing infestation of problematic Crack Willows that will eventually smother fish habitat and replace native riparian vegetation. These willows are currently at a level where they can be managed with good cost effectiveness but, if left for any longer, will become more and more difficult to control. Crack Willow are a particularly invasive type of willow which are difficult to control due to their multi-stem growth habit. Fortunately, there are skilled contractors who can effectively stem inject and kill these species while retaining their structure in situ. The infestation is currently at a level where they can be safely left as structural habitat and will break down over a number of years. This work will complement an associated Rivers of Carbon Macquarie perch project where a cluster of landholders either have, or are in the process of, fencing their section of the Murrumbidgee River from stock, installing alternative water sources and planting native vegetation to protect and enhance habitat for native fish and Platypus.  It will complement willow control activities that have been occurring upstream and downstream of the project site.

Fish hotels and habitat structures

This part of Restoring our Rivers – ‘After the fire’ will work in association with the willow control works being carried out to improve Macquarie perch habitat.  This species requires instream structure in its habitat for protection and is important at all stages of the lifecycle from young of year to mature fish.    Such structure, otherwise known as ‘snags’, is provided by native hardwood debris falling into the river from riverside vegetation.  Snags have historically been removed from our rivers, and the native vegetation which provides a source of snags has been historically cleared. Newly planted vegetation takes many decades before it is large enough to fall in and improve fish habitat.

This project will build and install a fish ‘hotel’ to improve fish habitat for Macquarie perch in the upper Murrumbidgee River.  The project site is just downstream of a breeding site for the species and is the known refuge area for the species.  Habitat improvement is a high priority for the species.  The hotels consist of log crib structures which are submerged into the river and filled with large sized rock.  This provides refuge for small fish from predation.